What is it? A free service that replaces your Internet provider's "domain name system" -- which is basically the stuff that servers do to get your browser to Google when you type in "www.google.com." (It's more complicated than that, but that's not something we need to get into now. Google explains here if you're interested in learning.)

The benefit to you: Speedier Internet access, better security, etc. The problem is that many ISPs don't put enough investment into DNS, resulting in Internet service that's not as quick as it could be. (Companies like OpenDNS have been offering these services for a long time. It's not mainstream, but it's not only something the geekiest of people do.)

The benefit to Google, if it can get people to use Google Public DNS: Happier Internet users!

But also, in theory, a bunch of data. Google would be able to know even more about what Web sites people are visiting than it does already.

The good news, if you care about privacy: It looks like Google isn't going to try to use that data for anything other than improving the DNS product.

Google says it will collect IP addresses ("only temporary") and ISP and location information (peramently) "for the purpose of making our service faster, better and more secure. Specifically, we use this data to conduct debugging, to analyze abuse phenomena and to improve our prefetching feature."

But Google says it does not store any of this information with your Google account, and does not share it with anyone else, including Google's own search, Gmail, or advertising services.

This is a lost business opportunity, but probably the only way Google would be able to get away with something like this. If they came out and said they'd be monitoring all your Internet activity and they'd be sharing it with advertisers, they'd probably get a ton of bad press. So this is a good decision.